The invention relates to the manufacture of submicron structures, in particular, to those of electronic components having dimensions lying between some nanometers and a few micrometers that exhibit component particles of submicron sizes (e.g. electrodes).
In its efforts to continuously decrease the sizes of integrated circuits and electronic components, research and development, in the mean time, turns its attention towards the physically smallest multicomponent structures. Such structures generally consist of a multitude of collections of material, arranged above and/or juxtaposed beside one another upon a substrate, whereby the dimension of such a collection lies in at least one dimension in the submicron range, say, thin layers, nano (sized) wires or quantum dots. The materials out of which the accumulations are formed vary from elemental metals through semi-conductors and metallic oxide ceramics up to organic compounds, e.g. functional or chemically stable polymers.
The precise arrangement of the various material components is essential for the predictability and reproducibility of the behavior of a submicron structure. If, for example, one now wants to arrange two electrically conductive nano wires—possibly made of different metals—in parallel, at a distance of a few 10 nanometers from one another on a substrate in order that a third metal—e.g. a dielectric material—can be inserted between these, then already misplacement of a couple of hundred metallic atoms could cause a short circuit and thus make the expensively produced structure unusable.
Here up until now, even the definitive arrangement of an individual nano wire has not long been a generally mastered art. Typical procedures that heretofore have been used distinguish themselves by their high costs, such as, for example, electron beam or photo lithography.
Nano wires (also quantum wires) exhibit typical lengths of some micrometers in connection with diameters in the nanometer range. Such wires offer the possibility of producing highly sensitive sensors, catalytically active surfaces or optically transparent electrical conductors.
The arranging or aligning of nano wires on a substrate is extremely difficult, since no suitable tools are available for a purpose-oriented manipulation of nano particles. Usual procedures for microstructuring, such as X-Ray lithography, fail in connection with quantum wires due to the fact that the required structural dimensions are distinctly smaller than the beam diameter, and the light cannot be focused without further ado. Many procedures, therefore, work towards self-organization of the metallic atoms or clusters upon the substrate, whereby the wires form by themselves. This can, however, be achieved only under very special conditions.
The ADELUNG, R et al, nature materials, Vol. 3, June 2004, p. 375-379 article describes a relatively simple method for placing a nano structure, in particular, a nano wire, upon a substrate, during which the nano wire follows a microscopic restructuring. For this purpose, the substrate is coated chemically in a wet state or by vapor deposition, e.g. with a brittle film of oxide or a polymer, and consequently, fissures are generated in this layer goal-specifically, that reach up to the substrate. For example, using vapor deposition, metallic atoms are finally placed onto the substrate with the fissured film, whereby wire formed collections of metal can build up directly on the substrate solely in the region of the fissure. If necessary, the film can be removed so that only these nano wires are left behind. Depending on the traced structure of the fissure, a nano wire network can thus also be produced, for example a rectangular lattice network.
The procedure presented in the above-mentioned article is indeed suitable for the simultaneous application of several materials, for example, for producing alloy wires made of element metals. If, however, one wants to create, as cited in the above-mentioned example, two metal wires, running parallel and electrically insulated from one another, then these, in accordance with the structural possibilities limited to the micro scale, will exhibit spacing of some 100 nanometers from one another.
A better proposal for producing immediately neighboring (juxtaposed) submicron structures using methods of microstructuring is given in U.S. Pat. No. 4,525,919. Here, the substrate is provided with a shadow mask and spattered with material at an angle against the normal (line) substrate. The shadow mask is realized through a hollow recess in one of the masking layers covering the substrate, whereby the free-lying substrate area is additionally shaded (shadow cast) by a second layer overlapping the first masking layer. The effective mask opening is thus smaller than the free-lying substrate area. Material input at an angle can only lead to a partial covering of the substrate. If the angle is altered, then regions of the “shadow space” on the substrate get covered. In particular, thus, separate nano wires running parallel can thus be obtained.
The problems of this procedure, indeed, lie in the necessary creation of the shadow mask. U.S. Pat. No. 4,525,919 provides for a combination of an epitactic growth of the mask and a selective etching in order to freely position the substrate in a (pre) defined area. Such measures are complicated to control, time-consuming and thus hardly suited for mass production.